Reconstructing the impact of COVID-19 on the immunity gap and transmission of respiratory syncytial virus in Lombardy, Italy

Alterations of pathogen transmission patterns and attenuated immune stimulation might be the cause of increased adult respiratory infections cases in 2023, results from a multi-center study in mainland China

Background

Several respiratory infections outbreaks have been observed in mainland China after reduction of non-pharmaceutical interventions. Other countries have seen increases in respiratory infections outside typical seasons post-COVID-19, warranting investigation into underlying causes.

Methods

We established monitoring networks for suspected respiratory infection in 14 tertiary hospitals nationwide. PCR for SARS-CoV-2, influenza A and B were performed on 3708 respiratory specimens and deep sequencing were conducted to identify co-infections or newly emerging microbes in 2023. Viral evolutionary analysis was completed. We retrospectively detected serum antibody level for various respiratory pathogens from 4324 adults without respiratory infections over 7 years to observe its dynamic curves.

Findings

SARS-CoV-2 and influenza A were the main pathogens during outbreaks in 2023, bacterial-virus and bacterial-bacterial co-infections were most detected, but community co-infections didn't significantly increase pneumonia incidence. Different SARS-CoV-2 and influenza variants were present in different outbreaks, and no novel pathogens were found. The epidemiological patterns of influenza A, COVID-19 and etc. were altered, exhibiting characteristics of being "staggered" compared to most global regions, and potentially led to "overlapping prevalence". Binding antibody testing showed regular fluctuation, without significant decrease against common respiratory pathogens in adults. Influenza A antibody stimulation was attenuated during the 2023 outbreak.

Conclusions

"Misaligned" alteration in seasonal respiratory disease patterns possibly caused combined epidemics, leading to cases spike in China, 2023. In adults, antibody levels didn't show significant decline, but reduced immune response to influenza during 2020-2023 emphasizes the need for consistent vaccination during pandemics.

Inconsistent Increase in Age at Respiratory Syncytial Virus Hospitalization of Children Aged <2 Years During the Severe Acute Respiratory Syndrome Coronavirus 2 Pandemic: A Retrospective Multicenter Study in 4 European Countries

BACKGROUND

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic disrupted respiratory syncytial virus (RSV) seasonality. To optimize the use and evaluation of RSV infant immunization strategies, monitoring changes in RSV epidemiology is essential.

METHODS

Hospitalizations for acute respiratory infections (ARIs) and RSV-coded ARI in children <2 years were extracted in 4 European hospitals, according to predefined case definitions (International Classification of Diseases, Tenth Revision codes). Prepandemic RSV seasons (2017-2018 to 2019-2020) were compared to 2021-2022 and 2022-2023.

RESULTS

In 2021-2022 and 2022-2023, the peak number of RSV hospitalizations was higher than prepandemic peaks after short periods of RSV circulation, and lower than prepandemic peaks after long periods of RSV circulation. A greater proportion of RSV hospitalizations occurred in children 1 to <2 years in 2021-2022 in the Netherlands (18% vs 9%, P = .04). No increase in age was observed elsewhere. High-risk children represented a greater proportion of RSV hospitalizations during the pandemic. The proportion of pediatric intensive care unit admissions did not increase.

CONCLUSIONS

A decrease in population immunity has been linked to older age at RSV hospitalization. We did not observe an increase in age in 3 of the 4 participating countries. Broad age categories may have prevented detecting an age shift. Monitoring RSV epidemiology is essential as Europe implements RSV immunization.

Increased Pediatric Respiratory Syncytial Virus Case Counts Following the Emergence of SARS-CoV-2 Can Be Attributed to Changes in Testing

BACKGROUND

Respiratory syncytial virus (RSV) circulation dropped markedly early in the COVID-19 pandemic, followed by a resurgence with heightened case counts. The "immunity debt" hypothesis proposes that the RSV-naїve pediatric population increased during the period of low transmission. However, the evidence supporting this hypothesis is limited, and the role of changing testing practices in the perceived surge has not been comprehensively evaluated.

METHODS

We conducted a multicenter, retrospective analysis of 342 530 RSV encounters and 980 546 RSV diagnostic tests occurring at 32 US pediatric hospitals in 2013-2023. We used interrupted time series analysis to estimate pandemic-associated changes in RSV patient and test volume and to quantify changes in the proportions of patients requiring hospitalization, intensive care, or mechanical ventilation. We quantified the fraction of the shifts in case counts and in the age of diagnosed patients attributable to changes in testing.

RESULTS

RSV patient volume increased 2.4-fold (95% confidence interval [CI]: 1.7, 3.5) in 2021-2023 relative to the pre-pandemic phase and was accompanied by an 18.9-fold increase (95% CI: 15.0, 23.9) in RSV test volume. Shifts in patient volume and in patient age were largely attributable to increased testing. The proportions of patients with RSV that required hospitalization, intensive care, or mechanical ventilation declined significantly across all patient age groups.

CONCLUSIONS

A surge in RSV testing, rather than in viral circulation, likely underlies the increased case counts observed in 2021-2023. These findings warrant a critical assessment of the immunity debt hypothesis and highlight the importance of considering the testing denominator when surveillance strategies are dynamic.

Impact of COVID-19 Pandemic on the Clinical Course and Complications of Varicella-A Retrospective Cohort Study

In this study, we aimed to characterize a cohort of children hospitalized due to varicella before and after the outbreak of the COVID-19 pandemic. Medical charts of all children hospitalized in the Regional Hospital of Infectious Diseases in Warsaw due to varicella in the years 2019 and 2022 were retrospectively analyzed and compared. In total, 221 children were included in the analysis; 59 of them were hospitalized in 2019, whereas 162 were hospitalized in 2022. Children hospitalized in 2022 were older than those reported in 2019 (median 4.0 vs. 3.0 years, p = 0.02). None of the hospitalized children received complete varicella vaccination. The most common complication in both years was bacterial superinfection of skin lesions, found in 156/221 (70.6%) of patients. This complication rate was higher in 2022 (50.8% in 2019 vs. 77.8% in 2022, p = 0.0001), OR = 3.38, 95% CI: 1.80-6.35. Moreover, skin infections in 2022 more often manifested with cellulitis (in 2022 13.6% vs. 3.4% in 2019, p = 0.03), OR = 4.40, 95% CI: 1.00-19.33. Sepsis as a complication of varicella was almost five-fold more prevalent in 2022 than in 2019 (p = 0.009), OR = 5.70, 95% CI: 1.31-24.77. Antibiotic use increased between 2019 and 2022 (71.2% vs. 85.2%, p = 0.01). Furthermore, patients were treated more frequently with the combination of two different antibiotics simultaneously (only 3.4% of patients in 2019 compared to 15.4% in 2022, p = 0.01). Primary infections with varicella zoster virus in 2022 led to a more severe course of the disease.

Birth characteristics as predictors of respiratory syncytial virus hospitalisation in newborns to optimise immunisation schedule

AIM

To examine birth characteristics that influence infant respiratory syncytial virus (RSV) hospitalisation risk in order to identify risk factors for severe RSV infections.

METHODS

Retrospective cohort study of 460 771 Sicilian children under 6 months old from January 2007 to December 2017. Hospital discharge records were consulted to identify cases and hospitalisations with International Classification of Diseases, Ninth Revision, Clinical Modification codes 466.11 (RSV bronchiolitis), 480.1 (RSV pneumonia) and 079.6 (RSV). RSV hospitalisation risk was estimated using adjusted odds ratios (aOR) and 95% confidence intervals (95% CI).

RESULTS

Overall, 2420 (5.25 per 1000 infants) RSV-related hospitalisations were identified during the study, with girls accounting for 52.8%. RSV hospitalisation risk increased for full-term, transferred, extreme immature, and preterm neonates with serious issues (aOR 3.25, 95% CI 2.90-3.64; aOR 1.86, 95% CI 1.47-2.32; aOR 1.54, 95% CI 1.11-2.07; and aOR 1.48, 95% CI 1.14-1.90). Compared to children born in June, the risk of RSV hospitalisation was significantly higher in children born in January (aOR 28.09, 95% CI 17.68-48.24) and December (aOR 27.36, 95% CI 17.21-46.99).

CONCLUSION

This study identified birth month and diagnosis-related groups as key predictors of RSV hospitalisations. This could help manage monoclonal antibody appropriateness criteria.

Estimated Impact of Nirsevimab on the Incidence of Respiratory Syncytial Virus Infections Requiring Hospital Admission in Children < 1 Year, Weeks 40, 2023, to 8, 2024, Spain

BACKGROUND

Data from the sentinel surveillance system of severe acute respiratory infections in Spain were used to estimate the impact of administration of nirsevimab to children born from 1 April 2023 onwards.

METHODS

Estimated RSV hospitalisations in < 1-year-olds during weeks 40, 2023, to 8, 2024, were compared to the number that would be expected after accounting for the background change in RSV circulation in the 2023/24 season, compared to 2022/23.

RESULTS

We estimated 9364-9875 RSV hospitalisations less than expected, corresponding to a 74%-75% reduction.

High burden of acute respiratory tract infections leading to hospitalization at German pediatric hospitals: fall/winter 2022-2023

PURPOSE

Given reduced immunity levels for seasonally occurring respiratory infections and the experience of an unusually early, severe wave of RSV infections during 2021, a preexisting clinician-led reporting system (CLRS) was updated to prospectively monitor the anticipated high burden of respiratory infections (ARI) in German pediatric hospitals during fall/winter 2022-2023.

METHODS

From September 13, 2022 through March 31, 2023, children hospitalized with ARI as a primary diagnosis were monitored via a national CLRS established by the German Society for Pediatric Infectious Diseases (DGPI). Once a week, the CLRS collected overall number of new hospital admissions, ARI-related admissions according to pathogen (SARS-CoV-2, RSV, influenza, and other), plus number of patients admitted to ICU with ARI as a primary diagnosis.

RESULTS

With a high participation among children's hospitals across Germany (22.8%), 76 centers submitted 1,053 survey reports. ARI-related hospital admissions showed a steep rise starting in late September 2022 and reached their highpoint in early December 2022 (50.1% of all admissions). In parallel, the average number of newly admitted patients (aNA) with RSV (3.6) peaked, as did those with influenza (2.1) one week later. The average highpoint of ARI patients on ICU (aICU) (2.9) was reached shortly thereafter. Again, RSV (1.6) und influenza (1.2) were predominant pathogens.

CONCLUSION

In fall/winter 2022-2023, German hospitals reported a sharp increase in patients with ARIs. While RSV and influenza represented the greatest proportion of ARI, SARS-CoV-2 played a less significant role. Systematic, dynamic collection of ARI data is critical for assessing real burdens on the health care system.

Respiratory syncytial virus-associated hospitalizations among children: an Italian retrospective observational study

BACKGROUND

Respiratory syncytial virus (RSV), a single-stranded RNA virus, is a leading cause of hospitalization in infants, especially ≤ 2 months of life. In the light new immunization strategies adoption, we described epidemiological and clinical characteristics of RSV-associated hospitalizations in pediatric and neonatal intensive care units of the Policlinico Foggia Hospital, Apulia Region, Italy.

METHODS

Hospitalized children with a laboratory-confirmed RSV infection from 2011 to 2023 were retrospectively evaluated. Clinical information was collected from Hospital Discharge Registry in the period 2011-2020. The proportion of the hospitalization for acute respiratory infections (ARIs) associated to RSV was calculated and the hospitalization cost was analyzed by using the diagnosis-related group reimbursement rate. The anticipated impact of immunization either with monoclonal antibodies or maternal immunization on the number of hospitalizations was estimated. All analyses and quality assessment were performed using STATA/SE15.0.

RESULTS

A total of 1,005 RSV-cases were included in the study, of which 86.3% occurred between December-March. In the period 2011-2020, 832 RSV-cases were matched with the corresponding hospital admissions; 75.2% were aged < 1 year (49.6% 0-2 months). Bronchiolitis was the most frequent admission diagnosis occurring in 63.3% of patients; 25% of children were affected by a very severe RSV-disease. Younger age ≤ 2 months (OR:14.8, 95%CI:8.30-26.31, p = 0.000), higher length-of-hospital-stay (OR:1.01, 95%CI:1.0-1.02, p = 0.030) and history of prematurity (OR:4.4, 95%CI:1.57-12.11, p = 0.005) were associated with a higher disease severity. RSV caused 48.9% of ARIs among children < 1 year. The mean cost of an RSV-associated hospitalization was 3,036 euros/year, with the higher cost in the 0-2 months age group (4,225 euros/year). Immunization programs with nirsevimab could prevent 51.4 RSV hospitalizations/year and 18.1 very severe RSV disease/year in infants < 1 year of age. RSV vaccine could prevent 46.1 of hospitalizations/year caused by RSV within 180 days after birth.

CONCLUSIONS

Our study contributes to outlining the baseline profile of RSV-associated hospitalizations among Italian children by providing epidemiological/clinical/economic estimates. While awaiting new recommendations on immunization, healthcare-workers should persist in implementing public health measures and appropriate case management to control RSV seasonal epidemics. Strengthened laboratory RSV surveillance is needed to inform the implementation of the new immunization strategies.

Increased pediatric RSV case counts following the emergence of SARS-CoV-2 are attributable to increased testing

Background

The incidence of respiratory syncytial virus (RSV) dropped markedly early in the COVID-19 pandemic, followed by a resurgence with heightened case counts. The "immunity debt" hypothesis proposes that the RSV-naive pediatric population increased during the period of low transmission, resulting in a subsequent increased risk of infection. However, the evidence supporting this hypothesis is limited, and no studies have comprehensively evaluated the role of changing respiratory viral testing practices in the perceived surge.

Methods

We conducted a multicenter, retrospective analysis of 342,530 RSV encounters and 980,546 RSV diagnostic tests occurring at 32 United States pediatric hospitals between 2013 and 2023. We used interrupted time series analysis to estimate pandemic-associated changes in RSV patient and testing volume, and to quantify changes in the proportions of patients admitted from the emergency department (ED), admitted to the intensive care unit (ICU), and receiving mechanical ventilation. We quantified the fraction of the observed shifts in case counts and in the age of diagnosed patients attributable to changes in RSV testing practices. Finally, we analyzed 524,404 influenza virus encounters and 1,768,526 influenza diagnostic tests to address the specificity of the findings to RSV.

Findings

RSV patient volume increased 2.4-fold (95% CI: 1.7, 3.5) in 2021-2023 relative to the pre-pandemic phase, and was accompanied by an 18.9-fold increase (95% CI: 15.0, 23.9) in RSV test volume. Over two-thirds of the apparent shifts in patient volume and in patient age were attributable to increased testing, which was concentrated among older pediatric patients. The proportions of patients with RSV requiring hospitalization, intensive care, or mechanical ventilation declined significantly across all patient age groups. These declines were not observed for patients with influenza virus.

Interpretation

A surge in RSV testing, rather than in viral circulation, likely underlies the increased case counts observed in 2021-2023. We identify expected consequences of increased testing, including the diagnosis of less severe cases and a shift in the patient age distribution. These findings warrant a critical assessment of the immunity debt hypothesis, while highlighting the importance of considering the testing denominator when surveillance strategies are dynamic.

Funding

National Institutes of Health & Howard Hughes Medical Institute.

Heterogeneity of influenza infection at precise scale in Yinchuan, Northwest China, 2012-2022: evidence from Joinpoint regression and spatiotemporal analysis

Identifying high-risk regions and turning points of influenza with a precise spatiotemporal scale may provide effective prevention strategies. In this study, epidemiological characteristics and spatiotemporal clustering analysis at the township level were performed. A descriptive study and a Joinpoint regression analysis were used to explore the epidemiological characteristics and the time trend of influenza. Spatiotemporal autocorrelation and clustering analyses were carried out to explore the spatiotemporal distribution characteristics and aggregation. Furthermore, the hotspot regions were analyzed by spatiotemporal scan analysis. A total of 4025 influenza cases were reported in Yinchuan showing an overall increasing trend. The tendency of influenza in Yinchuan consisted of three stages: increased from 2012 to the first peak in 2019 (32.62/100,000) with a slight decrease in 2016; during 2019 and 2020, the trend was downwards; then it increased sharply again and reached another peak in 2022. The Joinpoint regression analysis found that there were three turning points from January 2012 to December 2022, namely January 2020, April 2020, and February 2022. The children under ten displayed an upward trend and were statistically significant. The trend surface analysis indicated that there was a shifting trend from northern to central and southern. A significant positive spatial auto-correlation was observed at the township level and four high-incidence clusters of influenza were detected. These results suggested that children under 10 years old deserve more attention and the spatiotemporal distribution of high-risk regions of influenza in Yinchuan varies every year at the township level. Thus, more monitoring and resource allocation should be prone to the four high-incidence clusters, which may benefit the public health authorities to carry out the vaccination and health promotion timely.